1. Field of the Invention
The present invention relates to a radio base station transceiver sub-system which communicates with a mobile station by radio, and more particularly to a radio base station transceiver sub-system which distributes and allocates control channels and traffic channels to a plurality of base band signal processing blocks.
2. Description of the Related Art
As shown in FIG. 5, a radio base station transceiver sub-system (BTS) which communicates with a mobile station by radio comprises an amplifier block 1a, radio block 1b, base band signal processing blocks 1c1-1cn which process base band signals for a plurality of channels respectively, control block 1d, and an interface block 1e with a base station controller (BSC) 3.
The amplifier block 1a amplifies transmission/receive signals, and the radio block 1b converts frequencies from high frequency signals, which are input from an antenna via the amplifier block 1a, to base band signals, and converts the base band signals to high frequency signals and inputs the high frequency signals to the antenna via the amplifier block 1a. The base band signal processing blocks 1c1-1cn perform such processing as spread- and orthogonal modulation to a plurality of channels of communication signals (e.g. various control signals, voice signals) and inputs the modulated signals to the radio block 1b, and performs such processing as orthogonal detection, despread modulation and data demodulation to a plurality of channels of communication signals which are input from the radio block, and inputs the demodulated data to the interface block 1e. The interface block 1e performs signal multiple processing, signal separation processing and signal conversion processing between the base station transceiver sub-system (BTS)/base station controller (BSC). The control block 1d performs various controls, including call control, traffic channel setting control and transmission power management control.
A 20 msec frame of the traffic channel is divided into 16 radio frame offsets with an 1.25 msec interval, and the base band signal processing blocks 1c1-1cn execute signal processing of the traffic channels which are allocated in each radio frame offset unit. In each radio frame offset, the number of channels for which the base band signal processing block can process is limited. Therefore when a new traffic channel is allocated to a base band signal processing block, a base band signal processing block to which a traffic channel is allocated must be selected considering the load (number of channels) in the radio frame offset of each base band signal processing block.
Also as FIG. 6 shows, a radio zone ZN exists with the base station transceiver sub-system 1 as the center, wherein the radio zone is divided in a plurality of service areas (sector A, sector B, sector C), directional antennas 1a1, 1a2 and 1a3 are disposed in each sector respectively, and the base station transceiver sub-system 1 transmits/receives radio signals to/from the mobile stations 2a, 2b or 2c in the sector via the antenna.
In this way, the base station transceiver sub-system (BTS) 1 has a plurality of base band signal processing blocks 1c1-1cn for radio channels, and sets a control channel required for each sector using these base band signal processing blocks. To start the operation in sector units using the radio base station transceiver sub-system (BTS) 1, at least the following four control channels must be set for each sector.    (1) Pilot channel    (2) Sync channel    (3) Paging channel (downward control channel for paging/broadcasting information transmission)    (4) Access channel (upward control channel for transmitting call originating message or call incoming response messages from radio subscriber terminal)
In the paging channel and access channel, a plurality of channels can be set for each sector. How many control channels are set in a sector and which base band signal processing block handles each control channel are designated fixedly in advance by BTS operation data (station operation data).
Therefore conventionally control channels are set in each sector based on the station operation data, and the control channels of each sector are allocated to a predetermined base band signal.
Also the number of channels allocated to each base band signal processing block is monitored so that a new traffic channel and a control channel are allocated to a base band signal processing block which has few allocated channels.
When a base station transceiver sub-system (BTS) is opened, the available number of base band signal processing blocks may be low when the number of base band signal processing blocks disposed is low or is subject to a system failure. In such a case, it is judged whether decreasing the number of paging channels/access channels being set is necessary, and if not, it is necessary to cancel the allocation of control channels which are allocated to the base band signal processing block which cannot process, and to reallocate them to another base band signal processing block. If it is necessary to decrease, the number of control channels being set for each sector must be decreased and base band signal processing blocks must be reallocated.
Conventionally, however, a sector to which a control channel is allocated, the number of channels allocated, and a base band signal processing block to which a control channel of a sector is allocated, are designated fixedly by the station operation data of the base station transceiver sub-system. Therefore when the number of base band signal processing blocks is low at the opening of the base station transceiver sub-system (BTS), or when the number of available base band signal processing blocks is low due to a system failure, there is a case where the number of allocated control channels is decreased more than necessary, and the control channels are allocated to the base band signal processing blocks more than the processing capability.
Also when a traffic channel is allocated, a channel allocation position must be selected so that allocation does not concentrate to a same radio frame offset of a same base band signal processing block, in order to distribute the load of the base band signal processing blocks, and to decrease call loss probability. Conventionally, however, allocation was performed only under the conditions of a radio frame offset for each base band signal processing block without considering accurate load distribution.
The processing load of an individual channel constituting a control channel is different, and the processing load of a traffic channel is also different depending on the transmission rate. Conventionally a new traffic channel and a control channel are allocated simply to satisfy the conditions of a radio frame offset, without considering the processing load for each channel. Therefore if channels with a large load concentrate to a predetermined radio frame offset of one base band signal processing block, load in the radio frame offset increases, where processing capability is exceeded, call loss is generated, and call loss probability increases. To decrease call loss, hand off to another base station while a call is continuing must be possible. To enable a hand off, a base station which originated the hand off and a base station after a hand off must use a same radio frame offset. Therefore it is necessary to evenly distribute load to each base band signal processing block and to each radio frame offset considering the processing load of each channel.